1. Field of the Invention
This invention relates to a sprocket wheel having a plurality of replaceable or detachable teeth mounted to the wheel body.
2. Description of the Prior Art
A sprocket wheel having replaceable teeth is disclosed, for example, in Japanese Utility Model Laid-Open No. 1984-195246, which is shown in FIGS. 10 through 12, where the body 40 of the wheel has a plurality of notches 41 which are circumferentially regularly spaced from each other, each notch 41 having a pair of protrusions 42, 42 on both of its top sides. Each replaceable tooth is divided into a pair of parts 45, 45, each part 45 being provided with a tooth groove 46 on its upper surface which is used to engage with a chain (not shown), a pair of notches 47, 47 in both of its top sides which fit over the protrusions 42, 42 of the corresponding notch 41 of the body 40, a notch 48 in its bottom side which fits over the bottom 43 of the corresponding notch 41 of the body 40, and two bolt holes 49, 49 which are used to be threaded by bolts. Each pair of parts 45, 45 mounted to each notch 41 of the body 40 by facing each other, then fixed to the body 40 by bolts and nuts.
Another sprocket wheel having replaceable teeth disclosed in Japanese Utility Model Laid-Open No. 1989-53564 is shown in FIGS. 13 and 14, where the outer periphery of the body 50 is shaped into a circular form. Each replaceable tooth 55 comprises a tooth portion 56 which has a tooth groove 57 on its top surface, and a fixing portion 58 which is located under the tooth portion 56 and integrally formed with it. The replaceable teeth 55 are so disposed that they are regularly spaced from each other and that their fixing portions 58 are attached to one side of the wheel body 50. A bolt is inserted into a hole formed in the fixing portion 58 of each tooth 55 and into one of holes formed in the body 50, then each tooth 55 is fixed to the body 50 by each nut.
In the first-mentioned sprocket wheel, as each replaceable tooth is divided into two parts, a step or a gap may be formed between both tooth grooves of the parts. This creates a possibility that the chain engaging with the grooves is damaged.
In the last-mentioned sprocket wheel, as no notches are formed in the outer periphery of the body, driving or driven force exerted on the wheel is supported by the shearing stress acting on bolts. That is, excessive shearing stress may act on each bolt. With respect to axial thrust load on the sprocket wheel, a thrust load in one direction is sustained by the fixing portion of each replaceable tooth, but a thrust load in the other direction is sustained by bolts and nuts. That is, excessive tensile stress may act on each bolt and nut.
The object of the present invention is thus to provide an improved sprocket wheel having replaceable teeth each of which has an unsplit tooth groove, the wheel withstanding the circumferential driving force and axial thrust load. Other objects and advantages of the present invention will become apparent from the detailed description to follow taken in conjunction with the appended claims.